Syrian security forces attacked rebel-held suburbs of Damascus with fighter jets and rockets Sunday, killing at least ten people and wounding dozens in an offensive to stop rebels closing in on the capital.

The Britain-based Syrian Observatory for Human Rights said fighter jets carried out two airstrikes on the Damascus suburb of Daraya, while heavy rocket attacks pounded the nearby town of Deir al-Asafir, east of the capital, where most of the casualties took place.

Rebels are trying to push into the city center from their strongholds on the outskirts and fighting has been fierce. Forces loyal to President Bashar al-Assad have been trying to establish a secure perimeter around Damascus at all costs, turning the province into one of the main battlegrounds in the country's 20-month conflict.

The Observatory said the Syrian air force also launched airstrikes on the northern city of Aleppo as well as targets across northern Idlib province and the Mediterranean city of Latakia.

Also Sunday, a car bomb exploded near a mosque in a government-held district of the central city of Homs. Syria's state-run news agency said the attack killed 15 people and wounded 24. The Observatory reported that seven people died, but added that many of the wounded were in critical condition.

There was no immediate claim of responsibility.

Homs, Syria's third largest city, was one of the key centers of the armed uprising against President Assad.

Clashes around Damascus International Airport went into a fourth day Sunday. It has effectively been closed since Thursday when the army tried to push back rebels who say the entire airport road had become a battleground.